CL_FlushEntityPacket

In a multiplayer game of Quake, Quake 2, Quake 3 Arena or Half-Life (which was built on the Quake 1 engine), it prints this error in the right of your HUD whenever you've lagged behind the server you're connected to. It's usually preceded and followed by your character not moving or responding to any commands apart from looks.

Apparently, you can solve this problem by typing the following into the console. This didn't work for me, so YMMV.

If you go to PlanetHalfLife, there is apparently a patch available for the Windows modem software that should get rid of the problem altogether. One should always be skeptical when patching their system software for the sake of a single game, however.